Microelectronic devices, such as memory chips and microprocessor chips, typically include a microelectronic substrate die encased in a plastic, ceramic or metal protective covering. The die includes functional features, such as memory cells, processor circuits, and interconnecting circuitry. The die also typically includes bond pads electrically coupled to the functional features. The bond pads are coupled to terminals, such as pins, that extend outside the protective covering for connecting to buses, circuits and/or other microelectronic devices.
Conventional microelectronic devices are typically arranged side-by-side on a is circuit board or other support device that is incorporated into a computer, mobile phone or other larger electronic product. One drawback with this arrangement is that the circuit board may have a large surface area to accommodate a large number of microelectronic devices. Accordingly, it may be difficult to fit the circuit board into a housing of a compact electronic product.
One approach to address this problem is to stack one microelectronic die on top of another to reduce the surface area occupied by the dies. Typically, the stacked microelectronic dies are connected to each other with an intermediate adhesive layer that is heat cured to securely bond the dies to each other. However, the adhesive can have several drawbacks. For example, at high temperatures, the adhesive can emit gases that leave deposits on the bond pads of dies. The deposits can inhibit secure electrical connections between the bond pads and the terminals of the die. Another drawback is that the adhesive layer can have a different coefficient of thermal expansion than the dies to which it is attached. Accordingly, the adhesive layer can put stresses on the dies as the ambient temperature changes. In some cases, these stresses can crack or fracture the dies.